By Zencalcy Editorial TeamLast reviewed About us
A fall does not injure by itself; the injury comes from the force needed to stop the body. The shorter the stopping distance or time, the larger the average force. This calculator handles a drop with a known stopping distance, a known speed and stop time, or a known speed and stopping distance.
Average force in a fall, a car crash or any sudden stop.
Drop: F = m g (h + d) / d Stop time: F = m v / t Stop distance: F = m v² / (2 d)
These are average forces over the stopping interval. Real impacts peak higher than the average, especially when the deceleration is not uniform.
| Symbol | Meaning |
|---|---|
| F | Average impact force, in newtons. |
| m | Mass, in kilograms. |
| h, d | Drop height and stopping distance, in metres. |
| v, t | Impact speed and stopping time. |
The impact speed is √(2 × 9.80665 × 2) = 6.26 m/s. Stopping in 5 cm gives an average force of 10 × 9.80665 × 2.05 / 0.05 = 4,021 N, about 41 times the object's weight.
Continue with the Net Force Calculator, Normal Force Calculator, or the Rocket Equation Calculator — or browse more dynamics tools and all physics calculators.
The force is the momentum change divided by the stopping time. Bending your knees extends the stop from milliseconds to a fraction of a second, which lowers the average force proportionally.
Results are computed from the standard equations of classical mechanics. Unit conversions use the SI definitions published by NIST. Air resistance is ignored unless the calculator names a drag model.
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Last reviewed: September 2026. See how we build and check every tool on the about page.
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Content updated: September 2026